The present invention relates to a positive-working photoresist composition used in the photolithographic fine patterning works in the manufacture of semiconductor devices and the like in the electronics industry or, more particularly, to a positive-working photoresist composition of high sensitivity and high resolution capable of exhibiting high stability of the latent images formed by the pattern-wise exposure of the resist layer to actinic rays before the post-exposure baking (PEB) treatment.
As is well known, the photolithographic fine patterning work is a well established technology in the manufacture of various kinds of semiconductor devices such as ICs, LSIs and the like by using a photoresist composition. Namely, a photoresist layer of a photoresist composition is formed on the surface of a substrate such as a semiconductor silicon wafer and the photoresist layer is exposed pattern-wise to actinic rays through a pattern-bearing photomask to form a latent image of the pattern in the resist layer followed by a development treatment to form a patterned resist layer which serves as a protective layer in the processing of the substrate surface by an etching treatment or other means. The photoresist composition of the most conventional type is the positive-working photoresist composition comprising an alkali-soluble novolac resin as a film-forming agent and a naphthoquinonediazide group-containing compound as a photosensitizing agent.
Along with the rapid progress in recent years in the semiconductor technology toward a higher and higher degree of integration of the semiconductor devices with corresponding fineness in the patterning works leading to a submicron or quater-micron order of fineness in the photolithographic patterning for the manufacture of VLSIs and the like, the wavelength of the actinic rays used for the pattern-wise exposure of the photoresist layer should be shorter and shorter to shift from the so-called g-line to the wavelength regions of the so-called i-line and deep ultraviolet light and further to excimer laser beams such as KrF laser beams and so on. Deep ultraviolet light and excimer laser beams are used as a major current of the actinic rays for the pattern-wise exposure of resist layers in the photolithographic patterning works.
Conventional photoresist compositions comprising a novolac resin and a quinonediazide group-containing compound developed for use with g-line and i-line ultraviolet lights are not suitable for use with deep ultraviolet light or excimer laser beams due to the large absorptivity of ultraviolet having a shorter wavelength than g-line and i-line so that the so-called chemical sensitization-type photoresist compositions are now highlighted by virtue of the smaller ultraviolet absorption by the poly(hydroxystyrene)-based resin as the film-forming agent therein.
The above mentioned chemical sensitization-type photoresist composition utilizes a principle that the acid-generating agent contained therein as an essential ingredient releases an acid when the resist layer is pattern-wise exposed to actinic rays and the thus released acid catalytically acts on the resinous ingredient to alter the solubility thereof in a developer solution. Characteristically, the chemical sensitization-type photoresist compositions are advantageous in respects of their high pattern resolution and high sensitivity to actinic rays because even a small amount of an acid generated from the acid-generating agent exhibits a catalytic activity on the resinous ingredient. The chemical sensitization-type photoresist compositions can be classified into two classes of the positive-working photoresist compositions, in which the resinous ingredient is imparted with increased solubility in an aqueous alkaline solution as the developer solution by the catalytic activity of an acid, and negative-working photoresist compositions, which comprises an acid-generating agent, alkali-soluble resinous ingredient and crosslinking agent so that crosslinking of the resinous ingredient by the crosslinking agent is promoted by the acid generated by the irradiation with actinic rays to decrease the solubility of the resinous ingredient in a developer solution.
In view of the mechanism for the formation of a latent image by the activity of an acid released from the acid-generating agent on the solubility-reducing substituent groups in the resinous ingredient, a proposal is made for a chemical sensitization-type positive-working photoresist composition that an acid-capturing agent such as an amine compound is admixed in the composition with an object to prevent diffusion of the acid released from the acid-generating agent by the irradiation with actinic rays so as to improve the performance of the photoresist composition (see, for example, Japanese Patent Kokai 5-127369, 5-232706, 5-249662, 5-289322, 6-317902, 7-92678 and 7-120929).
Although addition of an amine compound with a chemical sensitization-type positive-working photoresist composition is in fact effective to some extent for the improvement of the pattern resolution, the effectiveness thereby is still insufficient to meet the fineness requirement in the patterning works for the manufacture of semiconductor devices of an extremely high degree of integration such as 64 megabits to 1 gigabit if not to mention the problem of an inherent decrease in the photosensitivity.
An alternative proposal is made in Japanese Patent Kokai 5-181279 and 7-92679 to admix the composition with a carboxylic acid compound with an object to increase the photosensitivity of the composition and to improve the cross sectional profile of the patterned resist layer obtained from the composition. This proposal, however, is not practicable because the improvement in the cross sectional profile of the patterned resist layer is insufficient in addition to the problem of a decrease in the pattern resolution.
Besides, a trouble is sometimes encountered in the photolithographic patterning of a resist layer that the patterned resist layer has a cross sectional profile which is not orthogonal but has trailing skirts, especially, when the substrate surface is provided with a high-reflectivity coating film of silicon nitride, titanium nitride, aluminum-silicon-copper alloys, tungsten and the like so that development is eagerly desired for a chemical sensitization-type positive-working photoresist composition which is not affected by such an undercoating thin film on the substrate surface.